Users are often required to login to authenticate their identity in order to access online accounts, computing devices, or other resources. Numerous authentication techniques exist. For example, before accessing a resource, a user may be required to provide a login name, email address, personal identification number (PIN), text-based password, picture password, digital certificate, physical access credential (e.g., smart card), phone number, biometric information (e.g., finger print, retinal scan, etc.), answers to one or more security questions, and/or other identifying information. Authentication has become a common requirement for almost everything users do on computers. Yet, authentication is a heavy and cumbersome task, often imposing a cognitive load (e.g., to remember passwords) or lengthy and cumbersome tasks (e.g., fingerprint/retinal scanning). Additionally, almost all existing authentication techniques require intentional movement on the part of the user (e.g., entry of a textual or picture password, placing a body part in proximity to a biometric scanner, etc.), which is difficult or impossible for many disabled persons. Still further, many existing authentication techniques are susceptible to being spoofed by humans and/or computers.